From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id B9A85CAC5BB for ; Thu, 9 Oct 2025 01:57:31 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1v6ftL-0000bY-Rj; Wed, 08 Oct 2025 21:56:27 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1v6ftG-0000av-7P for qemu-devel@nongnu.org; Wed, 08 Oct 2025 21:56:22 -0400 Received: from mx.treblig.org ([2a00:1098:5b::1]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1v6ftB-0003m5-FB for qemu-devel@nongnu.org; Wed, 08 Oct 2025 21:56:21 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=treblig.org ; s=bytemarkmx; h=Content-Type:MIME-Version:Message-ID:Subject:From:Date:From :Subject; bh=pA+Wk5omjMCa70hJHsYuBlSOynRYxrx0G2BCLz4bYLw=; b=Dnke1dtQ53KZuGo5 wuHDSFg05NNbotdsrCcpusgGMRnFksvKVDxrScSBbILdLMuAwBFbHV0aKTntHqEqFgQ/vaQfHCPRK 1YUkBPp8gZo6jZFklZ4sHha/RBMDBclhNlCBfhd3SHDrop5lbxOYCpeS6xrqHT/8KdddxSopkG9Lt bZLtUXYw0qvWLQmUc9fK77/yYkzH3UEGjnx8VfhWUx0HnJ79TXGLTYe9d6OkfNFwiGmKAIlA72/up x+dbqmcKqItZbIVXbKvT438fxTt4DDt/lsjRiTl7KxEmYTYXQkmLjISXgS/dDt0FbQYdSo+0TnXRe CCvvnNRsbf9+m4yWng==; Received: from dg by mx.treblig.org with local (Exim 4.96) (envelope-from ) id 1v6ft3-00FPH7-0s; Thu, 09 Oct 2025 01:56:09 +0000 Date: Thu, 9 Oct 2025 01:56:09 +0000 From: "Dr. David Alan Gilbert" To: Gerd Hoffmann Cc: qemu-devel@nongnu.org, Laurent Vivier , Marcel Apfelbaum , Markus Armbruster , Philippe =?iso-8859-1?Q?Mathieu-Daud=E9?= , Yanan Wang , Paolo Bonzini , Fabiano Rosas , Eric Blake , Eduardo Habkost , Zhao Liu Subject: Re: [PATCH v2] hw/uefi: add "info ovmf-log" + "query-ovmf-log" monitor commands Message-ID: References: <20251007135216.1687648-1-kraxel@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline In-Reply-To: <20251007135216.1687648-1-kraxel@redhat.com> X-Chocolate: 70 percent or better cocoa solids preferably X-Operating-System: Linux/6.1.0-34-amd64 (x86_64) X-Uptime: 01:52:24 up 164 days, 10:05, 2 users, load average: 0.05, 0.04, 0.00 User-Agent: Mutt/2.2.12 (2023-09-09) Received-SPF: pass client-ip=2a00:1098:5b::1; envelope-from=dg@treblig.org; helo=mx.treblig.org X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org * Gerd Hoffmann (kraxel@redhat.com) wrote: > Starting with the edk2-stable202508 tag OVMF (and ArmVirt too) have > optional support for logging to a memory buffer. There is guest side > support -- for example in linux kernels v6.17+ -- to read that buffer. > But that might not helpful if your guest stops booting early enough that > guest tooling can not be used yet. So host side support to read that > log buffer is a useful thing to have. > > This patch implements both qmp and hmp monitor commands to read the > firmware log. > > Signed-off-by: Gerd Hoffmann I'm OK with that, but I wonder if it would be better to have a command that wrote the buffer to a file rather than displaying it directly; I don't think we normally have anything else which outputs that much raw guest provided data directly. I assume when it goes wrong you end up with random unprintable junk in the buffer. Dave > --- > hw/uefi/ovmf-log.c | 237 +++++++++++++++++++++++++++++++++++++ > tests/qtest/qmp-cmd-test.c | 2 + > hmp-commands-info.hx | 13 ++ > hw/uefi/meson.build | 2 +- > qapi/machine.json | 10 ++ > 5 files changed, 263 insertions(+), 1 deletion(-) > create mode 100644 hw/uefi/ovmf-log.c > > diff --git a/hw/uefi/ovmf-log.c b/hw/uefi/ovmf-log.c > new file mode 100644 > index 000000000000..f7fdb1f6bcad > --- /dev/null > +++ b/hw/uefi/ovmf-log.c > @@ -0,0 +1,237 @@ > +/* > + * SPDX-License-Identifier: GPL-2.0-or-later > + * > + * print ovmf debug log > + * > + * see OvmfPkg/Library/MemDebugLogLib/ in edk2 > + */ > + > +#include "qemu/osdep.h" > +#include "qemu/units.h" > +#include "qemu/target-info-qapi.h" > +#include "hw/boards.h" > +#include "hw/i386/x86.h" > +#include "hw/arm/virt.h" > +#include "system/dma.h" > +#include "monitor/hmp.h" > +#include "monitor/monitor.h" > +#include "qapi/error.h" > +#include "qapi/type-helpers.h" > +#include "qapi/qapi-commands-machine.h" > + > + > +/* ----------------------------------------------------------------------- */ > +/* copy from edk2 */ > + > +#define MEM_DEBUG_LOG_MAGIC1 0x3167646d666d766f /* "ovmfmdg1" */ > +#define MEM_DEBUG_LOG_MAGIC2 0x3267646d666d766f /* "ovmfmdg2" */ > + > +/* > + * Mem Debug Log buffer header. > + * The Log buffer is circular. Only the most > + * recent messages are retained. Older messages > + * will be discarded if the buffer overflows. > + * The Debug Log starts just after the header. > + */ > +typedef struct { > + /* > + * Magic values > + * These fields are used by tools to locate the buffer in > + * memory. These MUST be the first two fields of the structure. > + * Use a 128 bit Magic to vastly reduce the possibility of > + * a collision with random data in memory. > + */ > + uint64_t Magic1; > + uint64_t Magic2; > + /* > + * Header Size > + * This MUST be the third field of the structure > + */ > + uint64_t HeaderSize; > + /* > + * Debug log size (minus header) > + */ > + uint64_t DebugLogSize; > + /* > + * edk2 uses this for locking access. > + */ > + uint64_t MemDebugLogLock; > + /* > + * Debug log head offset > + */ > + uint64_t DebugLogHeadOffset; > + /* > + * Debug log tail offset > + */ > + uint64_t DebugLogTailOffset; > + /* > + * Flag to indicate if the buffer wrapped and was thus truncated. > + */ > + uint64_t Truncated; > + /* > + * Firmware Build Version (PcdFirmwareVersionString) > + */ > + char FirmwareVersion[128]; > +} MEM_DEBUG_LOG_HDR; > + > + > +/* ----------------------------------------------------------------------- */ > +/* qemu monitor command */ > + > +typedef struct { > + uint64_t Magic1; > + uint64_t Magic2; > +} MEM_DEBUG_LOG_MAGIC; > + > +/* find log buffer in guest memory by searching for the magic cookie */ > +static dma_addr_t find_ovmf_log_range(dma_addr_t start, dma_addr_t end) > +{ > + static const MEM_DEBUG_LOG_MAGIC magic = { > + .Magic1 = MEM_DEBUG_LOG_MAGIC1, > + .Magic2 = MEM_DEBUG_LOG_MAGIC2, > + }; > + MEM_DEBUG_LOG_MAGIC check; > + dma_addr_t step = 4 * KiB; > + dma_addr_t offset; > + > + for (offset = start; offset < end; offset += step) { > + if (dma_memory_read(&address_space_memory, offset, > + &check, sizeof(check), > + MEMTXATTRS_UNSPECIFIED)) { > + /* dma error -> stop searching */ > + break; > + } > + if (memcmp(&magic, &check, sizeof(check)) == 0) { > + return offset; > + } > + } > + return -1; > +} > + > +static dma_addr_t find_ovmf_log(void) > +{ > + MachineState *ms = MACHINE(qdev_get_machine()); > + dma_addr_t start, end, offset; > + > + if (target_arch() == SYS_EMU_TARGET_X86_64 && > + object_dynamic_cast(OBJECT(ms), TYPE_X86_MACHINE)) { > + X86MachineState *x86ms = X86_MACHINE(ms); > + > + /* early log buffer, static allocation in memfd, sec + early pei */ > + offset = find_ovmf_log_range(0x800000, 0x900000); > + if (offset != -1) { > + return offset; > + } > + > + /* > + * normal log buffer, dynamically allocated close to end of low memory, > + * late pei + dxe phase > + */ > + end = x86ms->below_4g_mem_size; > + start = end - MIN(end, 128 * MiB); > + offset = find_ovmf_log_range(start, end); > + return offset; > + } > + > + if (target_arch() == SYS_EMU_TARGET_AARCH64 && > + object_dynamic_cast(OBJECT(ms), TYPE_VIRT_MACHINE)) { > + /* edk2 ArmVirt firmware allocations are in the first 128 MB */ > + VirtMachineState *vms = VIRT_MACHINE(ms); > + start = vms->memmap[VIRT_MEM].base; > + end = start + 128 * MiB; > + offset = find_ovmf_log_range(start, end); > + return offset; > + } > + > + return -1; > +} > + > +static void handle_ovmf_log_range(GString *out, > + dma_addr_t start, > + dma_addr_t end, > + Error **errp) > +{ > + g_autofree char *buf = NULL; > + > + if (start > end) { > + return; > + } > + > + buf = g_malloc(end - start + 1); > + if (dma_memory_read(&address_space_memory, start, > + buf, end - start, > + MEMTXATTRS_UNSPECIFIED)) { > + error_setg(errp, "firmware log: buffer read error"); > + return; > + } > + > + buf[end - start] = 0; > + g_string_append_printf(out, "%s", buf); > +} > + > +HumanReadableText *qmp_query_ovmf_log(Error **errp) > +{ > + MEM_DEBUG_LOG_HDR header; > + dma_addr_t offset, base; > + g_autoptr(GString) out = g_string_new(""); > + > + offset = find_ovmf_log(); > + if (offset == -1) { > + error_setg(errp, "firmware log: not found"); > + goto err; > + } > + > + if (dma_memory_read(&address_space_memory, offset, > + &header, sizeof(header), > + MEMTXATTRS_UNSPECIFIED)) { > + error_setg(errp, "firmware log: header read error"); > + goto err; > + } > + > + if (header.DebugLogSize > MiB) { > + /* default size is 128k (32 pages), allow up to 1M */ > + error_setg(errp, "firmware log: log buffer is too big"); > + goto err; > + } > + > + if (header.DebugLogHeadOffset > header.DebugLogSize || > + header.DebugLogTailOffset > header.DebugLogSize) { > + error_setg(errp, "firmware log: invalid header"); > + goto err; > + } > + > + g_string_append_printf(out, "firmware log: version \"%s\"\n", > + header.FirmwareVersion); > + > + base = offset + header.HeaderSize; > + if (header.DebugLogHeadOffset > header.DebugLogTailOffset) { > + /* wrap around */ > + handle_ovmf_log_range(out, > + base + header.DebugLogHeadOffset, > + base + header.DebugLogSize, > + errp); > + if (*errp) { > + goto err; > + } > + handle_ovmf_log_range(out, > + base + 0, > + base + header.DebugLogTailOffset, > + errp); > + if (*errp) { > + goto err; > + } > + } else { > + handle_ovmf_log_range(out, > + base + header.DebugLogHeadOffset, > + base + header.DebugLogTailOffset, > + errp); > + if (*errp) { > + goto err; > + } > + } > + > + return human_readable_text_from_str(out); > + > +err: > + return NULL; > +} > diff --git a/tests/qtest/qmp-cmd-test.c b/tests/qtest/qmp-cmd-test.c > index cf718761861d..ffdb7e979e0f 100644 > --- a/tests/qtest/qmp-cmd-test.c > +++ b/tests/qtest/qmp-cmd-test.c > @@ -52,6 +52,8 @@ static int query_error_class(const char *cmd) > /* Only valid with accel=tcg */ > { "x-query-jit", ERROR_CLASS_GENERIC_ERROR }, > { "xen-event-list", ERROR_CLASS_GENERIC_ERROR }, > + /* requires firmware with memory buffer logging support */ > + { "query-ovmf-log", ERROR_CLASS_GENERIC_ERROR }, > { NULL, -1 } > }; > int i; > diff --git a/hmp-commands-info.hx b/hmp-commands-info.hx > index 6142f60e7b16..eca0614903d1 100644 > --- a/hmp-commands-info.hx > +++ b/hmp-commands-info.hx > @@ -977,3 +977,16 @@ SRST > ``info cryptodev`` > Show the crypto devices. > ERST > + > + { > + .name = "ovmf-log", > + .args_type = "", > + .params = "", > + .help = "show the ovmf debug log", > + .cmd_info_hrt = qmp_query_ovmf_log, > + }, > + > +SRST > + ``info ovmf-log`` > + Show the ovmf debug log. > +ERST > diff --git a/hw/uefi/meson.build b/hw/uefi/meson.build > index 91eb95f89e6d..c8f38dfae247 100644 > --- a/hw/uefi/meson.build > +++ b/hw/uefi/meson.build > @@ -1,4 +1,4 @@ > -system_ss.add(files('hardware-info.c')) > +system_ss.add(files('hardware-info.c', 'ovmf-log.c')) > > uefi_vars_ss = ss.source_set() > if (config_all_devices.has_key('CONFIG_UEFI_VARS')) > diff --git a/qapi/machine.json b/qapi/machine.json > index 038eab281c78..329034035029 100644 > --- a/qapi/machine.json > +++ b/qapi/machine.json > @@ -1839,6 +1839,16 @@ > 'returns': 'HumanReadableText', > 'features': [ 'unstable' ]} > > +## > +# @query-ovmf-log: > +# > +# Find firmware memory log buffer in guest memory, return content. > +# > +# Since: 10.2 > +## > +{ 'command': 'query-ovmf-log', > + 'returns': 'HumanReadableText' } > + > ## > # @dump-skeys: > # > -- > 2.51.0 > > -- -----Open up your eyes, open up your mind, open up your code ------- / Dr. David Alan Gilbert | Running GNU/Linux | Happy \ \ dave @ treblig.org | | In Hex / \ _________________________|_____ http://www.treblig.org |_______/